The present invention relates to an end adapted for use on a pressurised container. In particular, the invention provides an easy open end suitable for use on a pressurised food can or the like. In a pressurised food can, the food product is inserted into the can and stored therein under pressure. The increased pressure in the can is achieved by pressurising the headspace above the food product.
This may be achieved in a number of different ways. For example, a droplet of liquefied, inert gas may be inserted into the can just prior to sealing, as described in U.S. Pat. No. 2,894,844. The liquid evaporates and the resultant gas pressurises the headspace. Alternatively, a portion of the can may be designed such that it can be irreversibly deformed inwardly. After filling the can and sealing the open end thereof, the deformable portion of the can is deformed inwardly, thereby reducing the volume of the headspace and pressurising the headspace gases. This technique is described in European Patent No. EP 0 521 642.
The advantage of pressurising a food can is that the can may be made of substantially thinner gauge metal, which is deformable under normal conditions. The increased internal pressure in the can helps to support the walls of the can, providing the rigidity required for handling and transport. The use of thinner gauge metal has significant cost benefits to the can manufacturer and also has significant environmental benefits.
Conventional food cans comprise a body, in which a food product is stored, and at least one separate end, which is connected to the free edge of the body, conventionally by seaming and in particular by a technique known as “double seaming”. Conventional ends comprise a flat plate-like centre panel connected to a seaming portion (often referred to as the “cover hook”) via a chuck wall, which supports a seaming chuck during the double seaming operation. At the base of the chuck wall a concave reinforcing bead (looking from the outside of the can) is normally provided, to strengthen the end and support the seam.
Some food cans are provided with an easy open end, which is connected to the can body in the same manner as a conventional end. An easy open end differs from the convention end in that a thinned score line is provided on the flat plate-like centre panel, around the periphery of a desired aperture. A tab is connected to the end, usually by a rivet, and the tab has a tail portion and a nose portion arranged on either side of the rivet. The tab is located on the plate-like centre panel with the nose portion overlying or adjacent to the thinned score line, defining the desired aperture. On opening, a consumer lifts the tail portion of the tab, which causes the tab to pivot (axially) about the rivet, pressing the nose portion against the score line area of the can end. This pressure causes the score line to rupture around the periphery of the aperture. The aperture panel may then be pulled free from the remainder of the can, allowing access to the contents of the container.
A container, whose contents are held under pressure, has the disadvantage that upon first opening by a consumer, the pressure inside the container is rapidly released to atmosphere and the stream of released gases may carry a quantity of product. This problem is particularly difficult when the product in the container is coloured and/or viscous, as this may spoil a consumers clothes, or where the product is potentially harmful to a consumer. This problem is referred to as “spurting” and is highly undesirable for the consumer. In extreme circumstances, such “spurting” may have explosive force making the can dangerous. The present invention is concerned with controlling “spurting” i.e. controlling the forceful ejection of headspace gases and entrained product particles upon first opening of a pressurised container.
A further problem with containers having so called easy open ends is that once rupture of the score line is initiated the rapid release of pressured gases from inside the container may result in uncontrolled severing of the score line, causing the aperture panel to missile. Such missiling is potentially very dangerous.